GMC Terrain EGR Vacuum Modulator Replacement at your home or office.

What is the EGR Vacuum Modulator all about?

Your vehicle’s exhaust gas recirculation (EGR) system is used to reduce your engine’s emissions by lowering the combustion chamber temperature. This produces less nitrous oxides, and burns pollutants contained in the exhaust gas that are reintroduced into the intake manifold. If the EGR valve opens and allows exhaust gases into the intake, the engine runs more smoothly and efficiently. However, this is not the case at idle, when the engine needs the most vacuum for proper operation.

If the EGR valve opens at idle, you can experience a rough idle and possibly a knock. Engine power is negatively affected at low RPM’s. Engineers implemented a control that closes the EGR valve when the engine is running at lower RPM’s. The engine produces lower vacuum at lower engine speeds, so it’s natural that the control is modulated by the engine’s own vacuum. The EGR vacuum modulator is a diaphragm that closes when the engine vacuum drops to idle, and opens as soon as the vacuum increases. It’s also known as a vacuum modulated valve. If the EGR vacuum modulator is leaking vacuum, is blocked internally, or is leaking, the Check Engine light will come on and the engine may start to knock.